Nanocomposites for orthopedic applications

Compared to relatively soft nanopolymers, nanocomposites may receive more interest in orthopedics due to their adjustable mechanical strength and stability, which are able to match the mechanical property of bone. In this section, nanocomposites are divided into several groups based on material characteristics and corresponding strategies associated with their applications. 

Another demonstrative example is the layered-scaffolds of BMP-incorporated HA nanocomposite for inducing osteogenesis and subsequent bone regeneration. A type of HA/chitosan/PAA nanocomposite, fabricated by the LbL technique introduced in 

Carbon-based nanocomposites refer to a class of composites modified or reinforced by carbon nanostructures such as carbon nanotube (CNT), carbon nanofiber (CNF), and particulate nanodimond (PND). Here, the strategy of utilizing carbon nanostructures, primarily CNT and CNF, to improve osteogenic property and bioactivity of the nanocomposites is primarily discussed. The strategy of promoting mechanical properties of orthopedic implants by creating carbon-based nanocomposites will be discussed in Chapter 5. 

Carbon nanofiber (CNF)/polyurethane Increasing osteoblast functions [56] 

Multiwall CNT/ultrahigh molecular weight extracellular calcium deposition, and upregulating mRNA expression for collagen type-I under electrical stimulation [54] Increasing cytocompatibUity of osteoblast- 

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Table 4.1 Carboii nanostructure-based nanocomposites for orthopedic applications...

Liu H, Webster TJ. Bioinspired nanocomposites for orthopedic applications. In Webster TJ, editor. Nanotechnology for the regeneration of hard and soft tissues. Singapore World Scientific Publishing 2007. p. 1-51. 

Li, H., Chen, Y, Xie, Y, 2003. Photo-crosslinking polymerization to prepare polyanhydride/ needle-like hydroxyapatite biodegradable nanocomposite for orthopedic application. Materials Letters 57, 2848-2854. 

Liu, H., Webster, T.J., 2007a. Bioinspired nanocomposites for orthopedic applications. In Nanotechnology for the Regeneration of Hard and Soft Tissues. World Scientific Publishing Company, Toh Tuck Link, Singapore. 

The biomimetic cement, GEMOSIL, consisting of gelatinous hydroxyapatite nanocomposite, calcium sihca, and calcium hydroxide particles, was developed for orthopedic applications by Ko and co-workers (1,2). 

Improvement in wear is frequently cited as a motivation for current composite research in UHMWPE for orthopedic implants [43, 44, 47—51]. Thus far, the use of fillers alone has not proven effective in reducing the wear rate of UHMWPE by an order of magnitude, as has been observed with extensive radiation crossfinking. Whereas conventional UHMWPE may have been the state of the art when early research on UHMWPE composites was initiated, today UHMWPE matrix composites need to demonstrate superior properties when compared with unfilled radiation crosshnked materials. Because the tribology of UHMWPE in artificial joints is strongly dependent on the kinematics and lubricant, additional research is needed to fuUy characterize the biotribological behavior of UHMWPE micro- and nanocomposites for specific orthopedic bearing applications. 

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